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Seaweeds are an important source of bioactive metabolites for the pharmaceutical industry in drug development. Many of these compounds are used to treat diseases like cancer, acquired immune-deficiency syndrome (AIDS), inflammation, pain, arthritis, as well as viral, bacterial, and fungal infections. This paper offers a survey of the literature for Gracilaria algae extracts with biological activity, and identifies avenues for future research. Nineteen species of this genus that were tested for antibacterial, antiviral, antifungal, antihypertensive, cytotoxic, spermicidal, embriotoxic, and anti-inflammatory activities are cited from the 121 references consulted.

The ocean environment contains over 80% of world’s plant and animal species [1] and with more than 150,000 seaweeds found in the intertidal zones and tropical waters of the oceans, it is a primary source of natural products [2].

Seaweeds are floating and submerged plants of shallow marine meadows. They have salt tolerance because the osmolarity of cytoplasm is adjusted to match the osmolarity of the seawater so that desiccation does not occur. They lack true stems, roots and leaves; however, they possess a blade that is leaf like, a stipe that is stem like, and a holdfast that resembles roots like terrestrial plants. Seaweeds contain photosynthetic pigments and use sunlight to produce food and oxygen from carbon dioxide, and the water [3].

Marine macroalgae are important ecologically and commercially to many regions of the world, especially in Asian countries such as China, Japan and Korea [4]. They are a valuable food resource which contains low calories, and they are rich in vitamins, minerals, proteins, polysaccharides, steroids and dietary fibers [5–7]. Since as early as 3000 BC, they were also considered important as traditional remedies [4]. The Japanese and Chinese use brown algae in the treatment of hyperthyroidism and other glandular disorders [8–11]. The unsaturated lipids afford protection against cardiovascular pathogens [12].

Seaweeds have been one of the richest and most promising sources of bioactive primary and secondary metabolites [13] and their discovery has significantly expanded in the past three decades [4,14,15]. The algae synthetize a variety of compounds such as carotenoids, terpenoids, xanthophylls, chlorophyll, vitamins, saturated and polyunsaturated fatty acids, amino acids, acetogenins, antioxidants such as polyphenols, alkaloids, halogenated compounds and polysaccharides such as agar, carrageenan, proteoglycans, alginate, laminaran, rhamnan sulfate, galactosyl glycerol and fucoidan [16–25].

These compounds probably have diverse simultaneous functions for the seaweeds and can act as allelopathic, antimicrobial, antifouling, and herbivore deterrents, or as ultraviolet-screening agents [26]. They are also used by the pharmaceutical industry in drug development to treat diseases like cancer, acquired immune-deficiency syndrome (AIDS), inflammation, pain, arthritis, infection for virus, bacteria and fungus [27]. Currently, algae represent about 9% of biomedical compounds obtained from the sea [28].

Compounds with cytostatic, antiviral, antihelmintic, antifungal and antibacterial activities have been detected in green, brown and red algae [29,30]. The algae produce pure forms of the fatty acids found in human milk that appear to be building blocks for mental and visual development [31] and have been extensively screened for syntheses of new drugs [32,33].

During the 1970s, Ryther and collaborators evaluated numerous species of red, green and brown macroalgae for their potential growth rates and dry weight yields [34]. They demonstrated that the genus Gracilaria was the most attractive candidate because of its ability to achieve high yields and while producing commercially valuable extracts [35].

Gracilaria Greville genus (Gracilariales, Rhodophyta) is a macroalgae group with more than 300 species of which 160 have been accepted taxonomically. These are usually red, green or greenish brown with a three-phase cycle and can be found in tropical and subtropical seas [36,37].

The Gracilaria species are important for the industrial and biotechnological uses because they have phycocolloids, the main source of agar α-(1,4)-3,6-anhydro-l-galactose and β-(1,3)-d-galactose with little esterification in cell wall [2,38]. Among the carbohydrates, agar and other polysaccharides are present in G. confervoides [39], G. dura [40], G. chilensi and G. secundata [41,42].

These algae also produce important bioactive metabolites like the primary compound with antibiotic activity acrylic acid [43], and the eicosanoids which are derivatives C20 polyunsaturated fatty acid (PUFA) metabolism through oxidative pathways that originate mainly from arachidonic acid and eicosapentaenoic acids, the precursors of prostaglandins (PGs) [44,45]. Species such as G. asiatica and G. lichenoids contain PGE2 [46,47]. PGF2 and 15-keto-PGE2 were respectively isolated from G. lichenoids and G. asiatica [45]; G. verrucosa contains PGA2 that appears to be responsible for a gastrointestinal disorder, known as “ogonori” poisoning in Japan [48].

Studies with G. asiatica reported the diterpenes cis and trans-phytol [63]. A variety of lactones are present in Gracilaria from the Pacific Ocean, such as aplysiatoxin isolated from G. confervoides [64,65], polycavernoside B, polycavernoside B2, and polycavernoside A2 and A3 isolated from G. crassa [49,66]. Other constituents are also containedin this genus such as proteins r-phycoerythrin from G. salicornia [67] and G. longa [68], gigartinine from G. chilensis [69] and proteoglycan from G. longa [70].

The possibility of finding new molecules from natural products is immeasurable. For this reason the plants and their derivatives are major sources of all drugs, affecting about 30% of pharmaceutical market [71]. According to Newman et al. (2003), between the years 1981 and 2002, 877 new molecules were introduced into the market, with 49% of substances isolated from natural sources followed by semi-synthetic derivatives or synthesized molecules taking the structures of natural origin as models [29].

The search for new effective medicines remains a challenge for scientists. Therefore around the world, many researchers have focused on natural sources for new molecules with algae among the targets of these studies. So in this study we reviewed the literature related to bioactivities for Gracilaria algae.

2. Results and Discussion

In this review, among the 160 species of Gracilaria already identified taxonomically, only 19 of them had their extracts and fractions chemically tested for toxicity, cytotoxic, spermicidal, antiimplantation, antibacterial, antiviral, antifungal, antiprotozoa, antihypertensive, antioxidant, anti-inflammatory, analgesic, and spasmolytic effects in gastrointestinal tract (Table 1).

These biological studies were mainly developed in Japan and Brazil. This fact is justified by the extensive coastlines and marine biodiversity and is influenced by several factors for the development of these species, such as temperature, radiation, salinity, metal ions and other chemically fundamental components. Australia and Guam have recently become interested in the study of algae and diverse marine species. The consumption of algae has increased in European countries in recent decades with 15 to 20 species of algae being marketed in Italy, France and Greece. In western countries like Venezuela, USA and Canada, the macroalgae are industrially used as a source of hydrocolloids agar, carrageenan and alginate [100]. Carrageenan has been found to be useful in ulcer therapy and alginates are known to prolong the period of activity of certain drugs [8–11].

There is currently a tendency to substitute the use of laboratory animals in toxicological tests with alternative methods to reduce their numbers in experiments, or refine the existing methodology in order to minimize pain and stress [105]. A rapid and effective alternative to realize primary toxicity and biological action screening of compounds is the estimation of the 50% lethal concentration (LC50) through brine shrimp assay using Artemia salina L. [106]. A 90% ethanol extract of G. domingensis had LC50 of 200 μg/mL against A. salina [74].

Another method to evaluate toxicity is determining cytotoxic activity. In this context aqueous extract from dried thallus of G. bursa-pastoris (10.0 μg/mL), chloroform and methanol extracts from G. textorii, which was isolated steroid cholest-4-en-3-one [107], and ethanol extract from G. verrucosa were not toxic in cell culture. However, aqueous extract from G. verrucosa at a dose of 1.2 mg/animal showed toxicity to mice [48], according to Table 1. In this seaweed, lipids were indentified, such as PGFα [84,85], glycerol, ethanolamine-phosphatidyl [58], choline-phosphatidyl [58,108], ethanol-phosphatidyl [58], floridoside [109], and carbohydrates, such as agar [110–113] (Figure 2).

2.2. Effects on the Nervous System

Studies related to nervous system are important to understanding and treat complex degenerative and behavioral diseases. 90% ethanol extracts from G. corticata, G. edulis and G. verrucosa did not cause central or periphery effects for mice or dogs (50 mg/kg), and did not show analgesic or anticonvulsant activities for mice [75] (Table 1).

2.3. Contraception Activity

The researchers have also investigated new molecules with anticonceptive action; the post-coital contraceptive action of marine seaweeds was also evaluated in animals. Methanol: methylene chloride (1:1) extract from G. corticata was orally administered at 500 or 1000 mg/kg/day to female rats from day 1 to day 7 of their pregnancies. Higher doses produced significant post-coital contraceptive activity due to enhanced pre-implantation without any marked side effects. These findings indicate that red marine algae are a potential source for post-coital contraceptive drugs [80].

90% Ethanol extracts from G. edulis (100 mg/kg) and G. corticata were inactivated before the antiimplantation effect when they tested in pregnant rats [75,80]. Ethanol extracts from shade dried thallus of G. edulis and G. verrucosa were inactive in spermicidal bioassays [75]. Extracts from G. edulis showed 100% inhibition of sperm motility and this effect was related to disruption of the plasma membrane by spermicidal compounds [3] (Table 1).

2.4. Anti-Inflammatory and Antioxidant Activities

The anti-inflammatory activity of seaweeds has been studied. Polysaccharide fractions from G. verrucosa at a dose of 4.0 mg/animal were orally and intraperitoneally administered to mice and showed immunopotentiating activity stimulating phagocytosis [82]. Methanol extract and polysaccharide fractions from G. verrucosa were also antioxidant [82,83]. Aqueous extract from G. textorii at a dose of 100 μg/mL did not inhibit platelet aggregation induced by adenosine diphosphate, arachidonic acid or collagen [81]. G. verrucosa, G. asiatica, G. lichenoides and others species contain PGE2 [47,85], that have physiological effects including hyperthermia, hypotension, smooth muscle dilatation, hyperalgesia and gastric secretion inhibition [114,115] (Table 1).

G. corticata and G. pygmea did not inhibit the growth of Aspergillus niger, Fusarium solani, Alternaria solani, or Penicillium funiculosum [91]. Petroleum ether, chloroform and methanol extracts from this seaweed at a concentration of 1.0 μg/units proved to be inactive on the inhibition of penicillinase enzyme [87]. From this specie, stearic lipids and capric acids were isolated [121] (Figure 5).

Some studies highlighting antiparasitic activity of seaweeds also were verified. 90 % ethanol extract from G. corticata and G. edulis were tested against Entamoeba histolytica and Plasmodium berghei and were not active [75].

2.8. Antivirial Activity

Extracts from G. bursa-pastoris and Gracilaria sp were inactive against the Herpes simplex 1 virus (HSV) and the human immunodeficiency virus (HIV) when evaluated in cell cultures [96]. Granin BP and citrullinyl-arginine proteins were isolated from these extracts [123,124]. Methanol extract from dried G. pacifica at a concentration of 200.0 μg/mL was active against Sindbis virus, but was not effective against H. simplex 1 when tested at a concentration of 400 μg/mL. Extracts and compounds obtained from Gracilaria sp with anti-HIV activity are also active against other retroviruses such as HSV. However, the pharmacodynamic mechanisms of the antiretroviral activity are still unknown because bioactive compounds from seaweed poorly investigated [9] (Table 1) (Figure 7).

3. Material and Methods

In this article, some reports about bioactivity of Gracilaria algae were reviewed in the specialized literature published up to January 2011. The search was carried out using data banks such as; Biological Abstracts, AlgaeBase, SciFinder Scholar, Pubmed and NAPRALERT (acronym for Natural Products ALERT-University of Illinois in Chicago, USA).

4. Conclusions

Algae are abundant in the oceans and represent a rich source of as yet unknown secondary metabolites. In this review, we found only a few studies with complete chemical profiles and pharmacological potential of the Gracilaria species. Most studies raised concerns about antimicrobial activity against Staphylococcus, Streptococcus, Candida and Herpes genus. Others referenced the cytotoxicity bioassays in which these algae species were not active, but they produce various types of prostaglandins and others substances that can be toxic to humans such as gastrointestinal disorders and lethality caused by G. verrucosa and G. edulis, respectively. To research new drugs it is necessary to evaluate other bioassay models to preserve the safety, efficacy and quality of the end products. In Brazil, there is a great need for toxicological, pharmacological, preclinical and clinical studies, as recommended by the RDC 48/2004.

Finally, we conclude that algae of the Gracilaria genus are a potential source for synthesis of new natural medicines. It is important to taxonomically classify and standardize extractions, while identifying the active compounds to attenuate possible environmental interference that could undermine the pharmacochemical profile, and thus generate different pharmacologic effects. In addition, it is important to sensitize corporate researchers and financial agencies to support this cause.